Instrumentation for recording and replicating orthopaedic implant orientation

ABSTRACT

An instrument for recording or replicating the orientation of an adjustable component of an implant with respect to a stem portion of the implant includes a base assembly configured to clamp the stem portion of the implant in a predetermined orientation, and a fixture supported on the base assembly in a predetermined orientation with respect to the base assembly, the fixture including a locking assembly configured to be adjusted in three dimensions and locked in a configuration which angularly locks an alignment tool relative to the fixture in the three dimensions when the alignment tool is engaged with the adjustable component and the adjustable component is operably assembled with the stem portion and the stem portion is clamped by the base assembly.

This application is a divisional of U.S. application Ser. No.13/597,840, filed Aug. 29, 2012 now U.S. Pat. No. 8,585,711 which issuedNov. 19, 2013, which is a divisional of U.S. application Ser. No.10/879,261, filed Jun. 29, 2004 now U.S. Pat. No. 8,273,093 which issuedSep. 25, 2012, the entire contents of which are both herein incorporatedby reference.

FIELD

The present disclosure relates to prosthetic devices particularlyshoulder prostheses and, more particularly, to a method and apparatusfor replication of angular position of a humeral head of a shoulderprosthesis.

BACKGROUND INFORMATION

The state of the prosthetic shoulder market has progressed such that asurgeon generally approaches shoulder replacement surgery according toone of two strategies. One strategy is to perform the shoulderreplacement surgery in accordance with a manufacturer's shoulderprosthesis or shoulder prosthesis product line. Particularly, a surgeonis provided with instrumentation and technique guidelines for theparticular shoulder prosthesis or prosthesis line. The guidelines and/orinstrumentation direct or dictate the angle of humeral head resectionfor the implant (prosthesis). This angle is in relation to the humeralintramedullary (IM) canal and is designed to match an optimum set ofangles already present in the design of the prosthesis.

Another approach is to perform the shoulder replacement surgery inaccordance with the patient's anatomy. Particularly, the humeral head isresected according to angles perceived to be “anatomic” in the opinionof the surgeon, not according to angles already present in theprosthesis itself. With this approach, the prosthesis is designed sothat its configuration is intraoperatively adjustable. This allows theprosthesis to be adjustable in situ so that it can match the bonypreparation.

Even with respect to these two divergent manners of surgical strategy, acommon problem in shoulder surgery is matching the humeral resectionangle across the articular margin to the predetermined angle designedinto the prosthesis. This angle may include the angle between aprosthetic collar and the diaphyseal section of the stem. In the case ofa collarless stem, the angle may inscribe the difference between thelongitudinal axis of the stem and the inferior surface of the prosthetichead. It is considered optimal for fixation and biomechanics if theresected angle and the angle of the prosthesis are identical, therebyallowing intimate contact between the superior surface of resected boneand the inferior surface of the implant.

Moreover, the angular version in which the prosthesis is implanted willhave a significant impact on the biomechanics of the prosthetic joint.Currently, most shoulder prosthesis systems on the market dictate thevarus/valgus angle of the bone cut. This strategy does not allow thesurgeon to intraoperatively match the implant to the patient'sbiomechanics after the prosthesis has been trialed, much less implanted.There are two known products currently marketed that attempt to resolveat least one of the above-noted issues. First, the Tornier-Aequalissystem provides a modular junction within the metaphyseal region of thestem which allows a small block between the stem and humeral head to beinterchanged. This block is available in multiple angles, thus allowingthe surgeon to select the block that best fits the bony anatomy asresected. This system, however, has two primary weaknesses. First, theuse of modular blocks obviously forces the design to only allow angularadjustments in finite increments. Second, the need to adjust the anglethrough modular blocks forces the surgeon to remove the stem, change outa component, and reset the stem.

A second product currently marketed provides a humeral head that isinfinitely adjustable in varus/valgus and anterior/posterior anglesrelative to the stem portion of the prosthesis. This is accomplishedthrough a spherical shaped protrusion on the superior surface of thestem that fits into a spherical recess in the humeral head. These matingsurfaces allow the head to be articulated about the stem, thus allowingadjustable positioning of the head. The head can be locked in a positionrelative to the stem. This solution provides the ability to adjust theneck-shaft angle as well as the version through flexibility in theanterior/posterior angle. The locking mechanism, however, is sub-optimalsince it requires the turning of a locking screw that has its headfacing lateral and inferior, for which there is no access once the stemhas been cemented. This eliminates the ability to adjust head positionon the fly, and forces a total revision if articular surfaces ever needto be revised. Lastly, the protrusion on the humeral stem even when thehumeral head is not in place limits the surgeon's access to the glenoidin preparation for a glenoid replacement.

It should be appreciated that it is desired to have a prosthesis that isintraoperatively adjustable so that it can match the bony preparation.One such prosthesis that has attempted to provide this design featureprovides a complicated and cumbersome jig to permit replication of thehead angular position between the trial prosthesis and the finalimplant. One problem with this jig is that the head position is takendirectly from the long axis of the humeral stem. Thus, the trial andimplant stems are required to adjust and replicate this position. Thismeans that the system has a large number of components to handle, andthe position cannot be adjusted with the stem in vivo. Another problemis that the jig itself is a quite complicated table-top device. The jigincludes an adjustment gage and a triplanar disc that must bemanipulated to effect replication of the head orientation between trialand final implant.

With a shoulder prosthesis that allows a surgeon to adjust the angularposition of the humeral head (i.e. adjust the articular surface of thehumeral head relative to the humeral stem/component and/or bone) amethod must be available for trialing the prosthesis. When the trialprosthesis is implanted, several adjustments can be made to set theangular position of the prosthetic head relative to the humeral stem. Ameans must be available for transferring the settings obtained duringthe trialing process to the final implant.

What is thus needed in view of the above is a better method for trialinga shoulder prosthesis, and more particularly for replicating theorientation of the trial implant components in the final implant. Thereis also a need for a replication system that is quick and easy tooperate, as well as for a system that can be utilized with implantsutilizing locking taper fixation.

SUMMARY

These and other needs are met by the present inventive recording andreplication instrumentation that is capable of replicating theorientation of a dialable component of an implant relative to the boneengaging component of the implant. For instance, the present inventionhas particular value in the preparation of a final humeral implanthaving a stem configured for fixation within the humerus bone and aspherical head that is “dialably” mounted to the stem—i.e., isadjustably mounted so the three-dimensional angulation of the head canbe adjusted as necessary for the particular patient anatomy.

The instrumentation contemplated by the present invention includes abase assembly for supporting the stem of a trial implant and a finalimplant, and a replication fixture that is supported on the baseassembly, preferably so that it can be removed. The base assemblyincludes means for supporting the stem of an implant with apre-determined datum in a pre-determined orientation. The same datum isused between the trial and final implants so that the configuration ofthe implant can be accurately repeated. The base assembly can include aclamp arrangement for clamping the implant stem in at least two degreesof freedom, and preferably in the medial-lateral, superior-inferior andanterior-posterior directions. The stem of the implant can include anarray of notches or grooves that are engaged by clamp elements of thebase assembly to fix the stem in those degrees of freedom.

The replication assembly is supported by several legs that are fixed tothe base assembly or most preferably are removably fit withincorresponding recesses in the base assembly. The replication assemblyincludes a guide member that supports an alignment tool. The alignmenttool is configured to engage the dialable aspect of the implant so thatthe tool “records” the angular orientation of the dialable aspectrelative to the datum. A locking mechanism locks the position of theguide member so that the alignment tool can be removed and replaced whena final implant is substituted in the base assembly. The alignment toolcan then be used to position the dialable aspect of the final implant.In one embodiment, the alignment tool is an impaction tool to impact thedialable aspect within the implant stem to lock the components togetherat the replicated orientation.

In accordance with one embodiment of the invention, a method is providedfor preparing an implant for implantation within a joint. The implantincludes a stem for implantation within a bone and a dialable componentmounted to the stem. In certain embodiments, the dialable component caninclude a head configured to engage an opposing portion of the joint,and a mounting assembly configured to fix the head to the stem invariable angular orientations to fit the joint anatomy. The inventivemethod comprises the steps of placing a stem of a trial implant within abone of the joint, positioning a dialable component on the stem of thetrial implant within the joint, using a jig to record an orientation ofthe dialable component relative to a pre-determined datum on the trialimplant, and using the same jig to replicate the orientation for adialable component of a final implant relative to the same datum on thefinal implant.

In certain aspects of the invention, the positioning step includesfixing the position of the trial dialable component relative to thedatum of the trial implant, and the recording step includes supportingthe trial implant within the jig with the datum in a predeterminedorientation. The recording step can further include fixing the trialimplant within the jig, using the jig to guide an alignment tool toengage the dialable component of the trial implant, and locking theangular orientation of the alignment tool relative to the jig when thealignment tool is in engagement with the dialable component.

The replicating step may include fixing a final implant within the samejig, using the jig to guide an alignment tool along the angularorientation obtained in the locking step, and manipulating the dialablecomponent of the final implant and the alignment tool until thealignment tool engages the dialable component of the final implant. Incertain embodiment, the replicating step includes fixing the dialablecomponent to the stem of the final implant. This fixing step ispreferably performed using the alignment tool. For instance, where themounting assembly of the final implant forms a press-fit engagementbetween the stem and the dialable component, the step of fixing thedialable component includes impacting the alignment tool to impact thedialable component into press-fit engagement with the stem of the finalimplant.

In certain embodiments, the dialable component includes a mountingassembly for mounting a head to the stem of the implant and the mountingassembly includes a fixed component fixed in the stem and a dialablecomponent capable of assuming various angular orientations relative tothe fixed component. In accordance with these embodiments, the datum isa predetermined axis passing through the fixed component. For example,the fixed component is a tapered bore and the datum is the centerlineaxis through the bore.

The present invention further contemplates an instrument for recordingthe position of a dialable component of an implant relative to apredetermined datum on a stem of the implant configured to be engaged ina bone. This instrument comprises, in certain embodiments, a baseassembly for supporting the stem with the datum in a predeterminedorientation, a fixture removably mountable on the base assembly whensupporting the stem, the fixture including an alignment tool forengaging the dialable component of the implant when the stem issupported by the base assembly, and a locking assembly for locking theangular orientation of the alignment tool relative to the fixture withthe alignment tool aligned with the dialable component so that thealignment tool defines an angular orientation of the dialable componentrelative to the datum.

The base assembly includes an assembly configured to clamp the stem tothe base assembly. Preferably, the assembly is a clamp assembly that isself-centering so that it is configured to center the stem relative tothe base assembly in at least two degrees of freedom. In one feature ofthe invention, the clamp assembly includes a v-shaped clamping elementconfigured to engage angled grooves defined in the stem.

In one feature of the inventive instrument, the locking assembly isconfigured to permit removal of the alignment tool after the angularorientation has been locked. The fixture may include a domed elementdefining an opening for extension of the alignment tool therethrough,and the locking assembly includes a guide member defining a bore forextension of the alignment tool therethrough, the guide member defininga spherical surface for nested engagement with the domed element. Insome embodiments, the guide member includes a post projecting from thespherical surface, the post defining the bore and the opening is sizedto receive the post therethrough to permit movement of the guide memberrelative to the domed element in at least two degrees of freedom.Preferably, the permitted movement relative to the domed element is aspherical angle. The post of the guide member includes external threadsand the locking assembly further includes a nut configured to engage theexternal threads. A washer can be provided between the nut and the domedelement with the dome surface disposed between the washer and thespherical surface of the guide member.

Preferably, the fixture includes at least one support leg and the baseassembly defines at least one recess corresponding to the at least onesupport leg for removable engagement of the leg therein. With thisfeature, the fixture can be removed to permit placement in or removal ofan implant in the base assembly.

It is one object of the invention to provide a system and method forreadily and easily preparing a final implant that accurately duplicatesthe orientation or configuration of a trial implant that has been usedto determine the proper implant configuration. Another object resides infeatures of the invention that ensure virtually identical replication ofthe position of a dialable component of an orthopaedic implant.

One benefit of the invention is that the inventive system and methodpermits use of standard trial and final implants. Another benefit isthat the final implant can be prepared apart from the patient withoutsacrificing an optimal anatomical fit for the implant, which can beespecially valuable where locking tapers are used.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is side elevational view of an exemplary shoulder prosthesis foruse with the present invention.

FIG. 2 is an exploded partial cross-sectional view of a portion of theshoulder prosthesis shown in FIG. 1.

FIG. 2 a is an exploded partial view of a modified head and dialablecomponent for use with the prosthesis shown in FIGS. 1-2.

FIG. 3 is a top perspective view of a portion of the shoulder prosthesisshown in FIG. 1.

FIG. 4 is a top perspective view of a base assembly for a recording andreplication instrument in accordance with one embodiment of the presentinvention.

FIG. 5 is a side perspective view of the base assembly shown in FIG. 4.

FIG. 6 is a side view of the base assembly shown in FIG. 4.

FIG. 7 is a top view of the base assembly shown in FIG. 4.

FIG. 8 is an end view of the base assembly shown in FIG. 4.

FIG. 9 is a side perspective view of a replication fixture for therecording and replication instrument in accordance with one embodimentof the present invention.

FIG. 10 is an exploded partial cross-sectional view of the replicationfixture shown in FIG. 9.

FIG. 11 is a side elevational view of a base assembly as depicted inFIG. 4 and a replication fixture as depicted in FIG. 9 forming therecording and replication instrument of one embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention.

For purposes of illustration, the preferred embodiment of the inventionis described in connection with a shoulder prosthesis, and particularlythe humeral component of the prosthesis. However, the inventive conceptsdisclosed herein can be used at other joints or bone interfaces of thebody. The common feature among these alternative uses of the inventionis that they include components that can assume a range of angularorientations relative to each other—angular orientations that must beduplicated from a trial implant or prosthesis to a final implant.

Referring now to FIG. 1 there is shown an exemplary embodiment of ashoulder prosthesis, generally designated 10. The shoulder prosthesis 10includes a bone-engaging portion or stem 12 terminating in a neck 14, aspherical head 16, and a mounting assembly 18 mounting the head to theneck. The stem is configured for implantation within a bone, such as thehumerus. The head 16 is configured to engage a mating joint component inthe glenoid of the shoulder joint. The mounting assembly is “dialable”,which means, in the context of the present invention, that the angularorientation of the head 16 relative to the stem 12 can be adjusted,preferably in multiple degrees of freedom. For instance, the head 16 canbe adjusted in the medial-lateral direction ML and the superior-inferiordirection SI or degree of freedom. This three-dimensional adjustabilityallows the implant to be configured to the particular patient anatomy.

The dialable mounting assembly provides a mounting interface between thestem neck 14 and the head 16. Preferably, the mounting assembly can beremovably engaged to both the stem and the head. In certain implants,the angular adjustment feature is situated between the mounting assemblyand the head. In other implants, the angular adjustment is effectedbetween the mounting assembly and the stem. For purposes of explanationof the present invention, this latter adjustability feature isillustrated. In particular, the mounting assembly contemplates a taperedbore 20 defined in the neck 14 of the stem 12. This tapered bore definesa centerline which is used as a datum D, as explained in more detailbelow. The bore terminates in a concentric threaded bore 22.

The tapered bore receives a spherical joint 24 that is configured to bepressed into the tapered bore to form a locking engagement. This lockingengagement can be enhanced by a mounting screw 30 that passes through aspherical seat 26 in the joint element and engages the threaded bore 22in the stem. Tightening the screw into the bore pushes the sphericaljoint element 24 further into the tapered bore 20.

In the illustrated embodiment, the head 16 is engaged to the mountingassembly 18 by a taper-fit engagement. In particular, the mountingassembly defines a tapered bore 28 to receive a complementary taperedpost 32 in a known manner. Alternatively, the head can incorporate thefemale locking component, as depicted in FIG. 2 a. In this alternativeconfiguration, the head 16′ includes a tapered bore 32′ that mates withthe tapered exterior 28′ of the mounting assembly 18′. The otherelements of the construction of the dialable elements can be the same asillustrated in FIG. 2.

It is understood that the implant 10 as thus far described can be atrial implant used to size and orient the components of the implant. Asis known, the associated bone is prepared to receive the stem 12 of theimplant. Thus, for the illustrated shoulder implant, the humerus bone isresected, broached and reamed to receive the stem 12 with the neck 14positioned in alignment with the glenoid component of the shoulderjoint. The head 16 is selected to mate with the glenoid component of thejoint, and the dialable mounting assembly 18 is adjusted to properlyposition the head on the neck within the shoulder joint. The implantcomponents are locked together so their relative angular positions arefixed. The trial implant is then removed and the orientation recordingand replication instrument of the present invention is used to duplicatethe trial configuration in a final implant.

In accordance with one aspect of the invention, the orientationrecording and replication instrument 110 (see FIG. 11) comprises a baseassembly 40 and a replication fixture 70 that is removably supported onthe base assembly. Referring to FIGS. 4-8, details of the base assembly40 will be discussed. In the illustrated embodiment, the base assemblyincludes two base halves 42 and 44 that are connected through a spacer46. Mounting bolts 48 pass between the two halves and through thespacers to form a solid support base construction. At least the basehalf 42, and preferably both halves 42, 44, are generally U-shaped todefine a slot 50. This slot 50 is sized to receive the stem 12 of animplant 10 passing therethrough when the implant is mounted within thebase assembly, as depicted in FIG. 11.

The base assembly 40 includes an assembly that is configured to engageand clamp the neck 14 of an implant (trial or final). In one aspect ofthe invention, this assembly includes a self-centering clamp assembly 51that is configured to clamp the implant to maintain a pre-determineddatum in a pre-determined and repeatable orientation. The datum is afixed location or axis on the implant that is common between the trialimplant and the final implant, and is used to establish a known startingpoint for replicating the position of the dialable components of theimplant. In the preferred embodiment, the datum is the central axispassing through the tapered bore 20 to which the dialable mountingassembly 18 mates. This datum is identified as the axis line D, as seenin FIGS. 2 and 11. As shown in FIG. 11, the base assembly 40 and clampassembly 51 are preferably configured so that the datum D is verticallyoriented when the implant 10 is supported by the base assembly. Ofcourse, other pre-determined orientations of the datum D can be used,provided that the orientation is repeatable between all trial and finalimplants.

In order to ensure repeatability of the orientation of the datum D, theself-centering clamp assembly 51 contemplates clamp elements integratedwith features on the implant itself. In particular, in accordance withthe preferred embodiment, the clamp assembly includes a rear clampelement 52 with a clamping edge 53 configured to engage a rear clampinggroove 37 (see FIGS. 2-3) defined in the neck 14. Similarly, the clampassembly includes a centering clamp element 55 that includes a generallyV-shaped clamping edge 56. This V-shaped edge is configured to engageangled grooves 35 defined in the neck 14 on the opposite side of theimplant from the rear groove 37 (see, FIGS. 2-3). The grooves 35, 37 andthe clamp elements 52, 55 are arranged so that the datum D isestablished at a pre-determined orientation when the implant is engagedby the clamp assembly 51. This pre-determined orientation of the datumis repeatable for every implant having similarly configured clampinggrooves 35 and 37.

The V-shaped edge 56 of the centering clamp element 55 ensures that theneck 14 is laterally centered within the base assembly—i.e., the neck iscentered along the axis L shown in FIG. 7. In accordance with thepreferred embodiment, the rear clamp element 52 is fixed to the basehalf 44 so that the rear clamping edge 53 has a fixed position in alongthe fore-aft axis F (FIG. 7). Thus, the rear clamp element establishesthe fore-aft position of the datum D when the rear clamping edge 53 isengaged within the rear groove 37 of the implant. In order to fix theimplant within the clamp assembly, the centering clamp element 55 isslidably mounted within the base half 42 so that centering clamp elementcan move along the fore-aft axis F.

In the illustrated embodiment, the centering clamp element 55 is carriedon a slidable carriage 58 that is disposed within a dovetail notch 60defined in the base half 42, as seen best in FIG. 4. The carriageincludes angled legs 62 that slide within the notch 60. A clamping nut64 bears against a plate 63 extending from the legs 62 so thattightening the nut pushes the centering clamp element 55 toward the rearclamp element 52. The clamping nut is threaded onto a clamping post 66that is mounted to the base half 42 by a drive plate 67 (FIG. 7-8). Asthe clamping nut 64 is rotated, it pushes against the drive plate 67 topush the carriage 58 along the dovetail notch 60 toward the implant neck14 until the V-shaped clamping edge 56 engages the angled grooves 35 inthe implant. As the clamping nut is tightened further, the V-shapedclamping edge manipulates the implant until the grooves 35 are centeredrelative to the clamping edge 56. At this point, the implant 10 isfirmly held on the base assembly 40 by the self-centering clamp assembly51 and the datum is automatically fixed in its pre-determinedorientation so that the angular position of the dialable elements of theimplant can be recorded.

The recording and replication feature of the invention is accomplishedusing the replication fixture 70 illustrated in FIGS. 9-10. The fixtureincludes a mounting platform 72 that is supported on the base assembly40 by legs 74. In one feature, the legs fit within recesses 69 (FIGS. 4,6-7) formed in the upper faces 43, 45 of the base halves 42, 44. Therecesses 69 and legs 74 are accurately sized so that the mountingplatform 72 assumes a pre-determined orientation relative to the baseassembly 40, the clamp assembly 51, and more importantly the implant 10supported by those two assemblies. Preferably, at least one of the legs74 and associated recesses 69 are indexed so the legs are placed in thesame orientation each time the fixture is removed and replaced on thebase assembly. For example, one leg and recess can be differently sizedform the other legs and recesses. In a specific embodiment, the indexedleg and recess have a smaller mating diameter than the other legs andrecesses. As a further alternative, one leg and one recess can include avisual indicia or the leg and recess can include a key between the twocomponents, such as a key and slot arrangement, to ensure that thefixture can be placed on the base assembly in only one orientation.

In the preferred embodiment, the replication fixture 70 is removablysupported on the base assembly 40, which can facilitate positioning andremoval of a trial or final implant within the base assembly. However,it is also contemplated that the replication fixture is essentiallyfixed to the base assembly—i.e., the base assembly and replicationfixture are one-piece or fastened together. It is also contemplated thatthe overall configuration of the base assembly and replication fixturewill depend upon the form of the implant being supported and replicated.

The replication fixture 70 utilizes an alignment tool 100 tointerdigitate with the dialable feature of an implant mounted within thebase assembly 40. The fixture further includes a locking assembly 75that is operable to lock the angular orientation of the alignment toolto the fixture once it has been oriented relative to the implant 10, asdescribed in more detail herein. The locking assembly 75 includes a dome76 integrated into the mounting platform 72. The dome defines an opening77 through which the alignment tool 100 extends. A spherical washer 80rides on the dome 75 with its inner surface 81 in contact with the outersurface 76 b of the dome. The washer also defines an opening 83 throughwhich the alignment tool extends.

The alignment tool is carried by a guide member 85 having a sphericalbase 86 that nests with the dome 76. In particular, the guide base 86includes an upper surface that bears against the inner surface 76 a ofthe dome. A cylindrical post 90 projects from the spherical base 86 ofthe guide member. The post includes external threads 91 and an internalbore 92. The bore is sized to slidingly receive the alignment tool 100therethrough. The opening 83 in the spherical washer 80 is sized toclosely receive the post 90 therethrough. The opening 77 in the dome 76is larger in size to permit angulation of the guide member 85 relativeto the mounting platform 72.

In a specific embodiment, the post 90 of the guide member has an outerdiameter of 0.875 inches, while the opening 83 in the washer has adiameter of 0.895 inches. On the other hand, the opening 77 in the domehas a diameter of 1.75 inches, or twice the diameter of the guide post,which will permit nested movement of the guide member 85 relative to thedome through a spherical angle of about ten degrees.

As shown in FIG. 10, the three components are successively assembled sothat the dome 76 is sandwiched between the spherical washer 80 and thespherical base 86 of the guide member 85. This construction ensurescontrolled movement of the guide member and alignment tool relative tothe fixed datum D of the implant 10 clamped within the base assembly 40.In other words, the construction only permits spherical angulation,while preventing transverse shifting of the tool relative to the datum.

The locking assembly 75 further includes a locking nut 94 with internalthreads 95 to engage the external threads 91 of the guide post 90. Thelocking nut includes a face 96 that bears against a flat 82 of thespherical washer 80. When the nut is tightened it draws the washer andspherical base 86 of the guide member together with the dome 76therebetween. When tightened enough, the nut 94 essentially locks theposition of the guide member relative to the mounting platform 72 and tothe base assembly 40, and ultimately to the datum D that was fixedrelative to the base assembly when the implant was clamped in place bythe self-centering clamp assembly 51.

It can be seen from the foregoing description that the two components ofthe instrument 110, namely the base assembly 40 and the replicationfixture 70, work together to: a) establish a datum D on the implant thatis fixed regardless of the implant; b) provides a movable guide memberfor an alignment tool; and c) provides means for locking the guidemember once its position relative to the datum has been established bythe alignment tool.

These features can be understood with reference to FIG. 11. Once thetrial implant has been configured in situ it is removed from the patientand placed within the base assembly 40. In particular, the neck 14 ofthe implant is positioned within the self-centering clamp assembly inthe orientation shown in FIG. 11. In this position, the stem 12 extendsthrough the slot 50 in the base half 42 so the datum D can be verticallyaligned in its fixed position. The head component can be removed,leaving the dialable mounting assembly 18 in the orientation achievedduring trialing.

With the trial implant clamped in place, the replication fixture 70 isplaced on the base assembly 40 with the legs 74 seated within thecorresponding recesses 69 in the base halves 42, 44. The fixture 70 isthus positioned above the implant and more specifically above thedialable mounting assembly 18 (or the assembly 18′ depicted in FIG. 2a). The alignment tool 100 is inserted through the bore 92 in the guidemember post 90. The tool includes a guide shaft 102 with a diametersized for close running fit within the bore 92. The tool 100 is providedwith an insertion tip 103 at one end and a handle 105 at an oppositeend. With the tool extending through the guide member, the handle 105 ismanipulated until the tip 103 can be inserted into the tapered bore 28in the mounting assembly 18. The tip 103 can be appropriately sized toform a tight, but removable, fit with the bore 28. Once the tip isfirmly engaged with the mounting assembly, the locking assembly 75 canbe manipulated to lock the position of the guide member relative to themounting platform 72 and the datum D. Specifically, the nut 94 can bethreaded onto the post 90 to tighten the spherical washer 80, dome 76and spherical base 86 together. The alignment tool 100 is then removed.

The replication fixture can now be removed from the base assembly. Thetrial implant is removed from the clamping assembly and a final implantis positioned within the base assembly. It is understood that the finalimplant is substantially similar to the trial implant so that the datumD on the final implant will have the same orientation within theshoulder joint as the trial implant. Moreover, it is understood that thetrial and final implants include the same configuration of the rearclamping groove 37 and the angled grooves 35 so that when any implant isfixed within the self-centering clamp assembly 51 the datum Dconsistently achieves the same orientation. Without this control, thetrial orientation of the dialable components of the implant cannot beaccurately replicated.

The final implant is lodged within the clamp assembly 51 in the samemanner as the trial implant so that the datum D is in the verticalorientation shown in FIG. 11. The same replication fixture 70 is nowplaced onto the base assembly with the guide member 85 in the clampedposition it was placed in when aligned with the trial implant. The samealignment tool 100 is introduced into the bore 92 of the guide member 85and is manipulated until the insertion tip 103 engages the tapered bore28 of the dialable mounting assembly. It is understood that the dialablecomponent of the mounting assembly is loosely disposed within thetapered bore 20 in the neck 14 of the final implant. Thus, once theinsertion tip contacts the tapered bore 28, manipulation of thealignment tool will alter the angular orientation of the dialablecomponent. When the tip is fully seated within the bore 28, the positionof the dialable component of the final implant exactly replicates thetrialed position. The dialable component can then be fixed within theimplant.

In accordance with the illustrated embodiment, the dialable componentrelies upon a taper fit between the dialable component and the taperedbore 20. In particular, the position of the dialable component isestablished when the spherical joint 24 is pressed into the tapered bore28. In order to facilitate this press-fit engagement without sacrificingthe replicated orientation, the present invention contemplates that thealignment tool 100 also serves as an impacting tool. Thus, the handleincludes an impaction end 106 that can be struck by a mallet. Theinsertion tip 103 is hardened so that it can transmit the mallet impactinto a force driving the spherical joint 24 into the tapered bore 20.Once the dialable mounting assembly is firmly seated, thealignment/impaction tool 100 can be retracted and the entire replicationfixture 70 removed from the base assembly.

The fixation of the dialable component of the mounting assembly can becompleted in accordance with the assembly—i.e., the mounting screw 30can pass through the spherical seat 26, with the spherical head engagedwithin the sear, and into the threaded bore 22 of the neck 14. Inaddition, the head 16 can be added to the implant while the implant isstill held within the clamp assembly 51. Once the final implant has beenassembled it can be removed from the base assembly 40 and implantedwithin the patient's shoulder joint. It should be understood that thepresent invention can be utilized with other means for fixing orengaging the dialable components other than the taper-fit or press-fitengagement described above. Moreover, it is understood that theimpaction aspect of the invention can be utilized on other forms offixation, such as interdigitating elements or teeth, to complete theassembly. In addition, the engagement can be by threading or similarmechanism, in which case the impaction tool would be appropriatelyconfigured to accomplish the threaded engagement.

The instrument 110 provides s simple and easily managed device forreplicating the orientation of dialable components of an orthopaedicimplant. In accordance with the preferred embodiment, the implant itselfincorporates landmark features that are fixed relative to apre-determined datum and that are keyed on to clamp and support theimplant with the datum in a known and repeatable orientation. In otherwords, in accordance with the illustrated embodiment, the neck 14 of theimplant 10 (both trial and final) is provided with clamping grooves 35and 37. Moreover, the clamping assembly includes clamp elements 52 and55 that are configured to lodge within these corresponding grooves. Itis understood, however, that the implant can be provided withalternative landmark features and that the clamp elements can beappropriately configured to key on the alternative landmarks.Furthermore, the clamp elements can be configured to key on existingfixed and repeatable landmark features that are integrated into theexisting implant design. It is important that the clamp assembly be ableto achieve repeatable positioning of the same datum on any implant,whether trial or final.

The illustrated embodiment also contemplates one type of dialablecomponent for a mounting assembly to mount a humeral head to the stem ofa humeral implant. Of course, other implants include other types ofdialable components of the implant with other types of clampingmechanisms to fix the position of the dialable component. For instance,in certain embodiments, the dialable component is integrated into thehumeral head itself—e.g., the spherical joint 24 is integral with theunderside of the head 16. If this modified head is configured to accepta mounting screw, such as the screw 30, then the head will include abore, like the bore 28, that can be engaged by the alignment tool 100 inthe manner described above.

In other embodiments, the dialable component of the mounting assemblymay not be configured to mate with the insertion tip 103 of thealignment tool 100 described above. It is contemplated that the workingend of the alignment tool 100 be configured as necessary to engage thedialable component when fixed within a trial implant and when looselysituated within a final implant. For example, the dialable component mayinclude a stem and the working end of the alignment tool can include abore configured for a tight fit with the stem.

The alignment tool 100 can also include an alignment groove 108 definedin its working end. The alignment groove can mate with a correspondingkey in the dialable mounting assembly. The key and groove can be used tolocate a rotational angle or to perform a rotating driving function,such as to fix a threaded engagement.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

What is claimed is:
 1. An instrument for recording or replicating the orientation of an adjustable component of an implant with respect to a stem portion of the implant, comprising: a base assembly configured to clamp the stem portion of the implant in a predetermined orientation; and a fixture supported on the base assembly in a predetermined orientation with respect to the base assembly, the fixture including a locking assembly configured to be adjusted in three dimensions and locked in a configuration which angularly locks an alignment tool relative to the fixture in the three dimensions when the alignment tool is engaged with the adjustable component and the adjustable component is operably assembled with the stem portion and the stem portion is clamped by the base assembly.
 2. The instrument according to claim 1, wherein the base assembly includes a clamp assembly configured to clamp the stem portion.
 3. The instrument according to claim 2, wherein the clamp assembly is configured to center the stem portion relative to the base assembly in at least two degrees of freedom.
 4. The instrument according to claim 3 wherein the clamp assembly includes a v-shaped clamping element configured to engage angled grooves defined in the stem portion.
 5. The instrument according to claim 3, wherein the fixture is removably supported on the base assembly in the predetermined orientation.
 6. The instrument according to claim 5, wherein the base assembly and the fixture define a keyed relationship which defines the predetermined orientation.
 7. The instrument according to claim 1, wherein the locking assembly is configured to permit removal of the alignment tool while the locking assembly is locked.
 8. The instrument according to claim 1, wherein: the fixture includes a fixed domed element defining a domed element opening; and the locking assembly includes a guide member with (i) a base portion configured to abut an inner surface of the domed element, and (ii) a post configured to extend from the base portion through the domed element opening.
 9. The instrument according to claim 8, wherein: the post defines a post opening sized to receive at least a portion of the alignment tool therethrough.
 10. The instrument according to claim 9, wherein: the post includes a threaded portion; and the locking assembly further includes a nut configured to engage the threads.
 11. The instrument according to claim 10, wherein: the locking assembly further includes a washer configured to be positioned about the post and abut an outer surface of the domed element.
 12. The instrument of claim 11, wherein: the base portion includes an arcuate surface shaped complementary to the inner surface of the domed element; and the washer includes an arcuate surface shaped complementary to the outer surface of the domed element.
 13. The instrument of claim 12, wherein the base assembly includes a clamp assembly configured to clamp the stem portion.
 14. The instrument according to claim 13, wherein the clamp assembly is configured to center the stem portion relative to the base assembly in at least two degrees of freedom.
 15. The instrument according to claim 14 wherein the clamp assembly includes a v-shaped clamping element configured to engage angled grooves defined in the stem portion.
 16. The instrument according to claim 14, wherein the fixture is removably supported on the base assembly in the predetermined orientation.
 17. The instrument according to claim 16, wherein the base assembly and the fixture define a keyed relationship which defines the predetermined orientation.
 18. The instrument according to claim 17, wherein the locking assembly is configured to permit removal of the alignment tool while the locking assembly is locked. 